The present invention relates to the use of a polymer in a method of treatment in which it is introduced into a body cavity under conditions whereby insoluble polymer is deposited in the body cavity. In the invention polymer having pendant zwitterionic groups is used, whereby biocompatibility is optimised.
The current chosen method for the treatment of aneurysms involves the packing of the aneurysm with platinum coils. Some work has been performed on the coating of these coils to provide a surface with increase thrombogenicity and render it biologically active by enabling the release of cellular growth factors and the like (German Patent DE-A-19647280). Others have concentrated on the use of polymer systems for embolising aneurysms, often simply by precipitating the polymer from a solution in a biocompatible solvent (WO-A-9745131). Specifically, a Japanese Group has had some success using a liquid composition containing a hardening polymer (cellulose acetate), with an X-ray contrast agent in a solvent such as DMSO. The polymer is caused to precipitate in-situ within the aneurysm when contacted with blood (JP-A-06-107549, J. Neurosurg., 83(3), 531, 1995). Another approach has been to directly polymerise monomers in-situ, an example of which is a iron-acrylic compound which polymerises rapidly and is non-toxic (J.Neurosurg., 47(2), 137, 1977). Yet another approach described in U.S. Pat. No. 5,749,894 is to introduce a coil and a polymeric composition which is melted by incident radiation and re-solidified in situ in the aneurysm. Examples of polymers are polyalkenes, poly(meth)acrylates, polyesters, polyamides and polysaccharides.
The use of polyion complexes in medical applications has been suggested for many years. Indeed, Michaels made reference to the use of such complex solutions for potting or encapsulating aneurysms, commenting that the materials were reasonably well tolerated by the tissue. Ioplex 101 (a complex poly(triethyl-(3 and 4)-vinylphenylammonium bromide) and poly(sodium vinyl benzenesulphonate)) has been examined intensively for biomedical usage (Vogel et al. J.Macromol. Sci., Chem., 4, 675, 1970; Marshall et al., J. Biomed Mater. Res., 4, 357, 1970; Bruck et al., Ann. N.Y. Acad Sci., 283, 332, 1977). Analogues of this system have been studied to determine the effect of charge and structure on the complex and their behaviour towards blood platelets (Kataoka et al., Makromol. Chem., 179, 1121, 1978 and 181, 1363, 1980) and have been used as encapsulating agents in the development of artificial liver support systems (Kataoka et a., Jinko Zoki (Artificial Organs), 8 296, 1979).
Nakabayashi et al. have previously described the use of polyion complexes of polymers having zwitterionic pendant groups for the selective adhesion of platelets (J. Biomed. Mater. Res., 28(11), 1347, 1994 by Ishihara, K. et al. Adv. Biomat. Biomed. Eng. Drug Delivery Syst. (1995) 227-228 by Ishihara, K. et al., and Japanese Patent JP-A-7-238124). Their invention claims specifically the use of a ternary polymer system consisting of 2-methacroyoyloxyethyl phosphorylcholine (MPC), butyl methacrylate (BMA) and sulfopropyl methacrylate (SPM) or trimethyl ammonium propyl methacrylate (TPM). Further to this, they define the compositions in which the MPC:BMA molar ratio is between 2:98-50:50, and the ratio of these two components to the ionic monomer (SPM or TPM) is between 98:2-80:20. These systems seem to have been designed to produce coatings with weak ionic interactions that have favourable properties in terms of platelet binding and activation. The polyion complexes described in these references are tested as coatings on glass beads and one of the products is said to be under test for use to encapsulate activated charcoal used for an artificial liver support system.
In the present invention there is provided a new use of a charged polymer in a method of manufacture of a composition for use in the method of treatment of a human or animal by therapy or diagnosis in which the charged polymer containing composition is introduced into a body cavity and is contacted with a separate composition comprising a polyvalently charged counterion whereby the polymer is rendered insoluble in the body cavity, and is characterised in that the charged polymer has zwitterionic pendant groups.
The present invention also includes the method of treatment itself.
In the present invention, the insoluble polymer is deposited as a gel in the body cavity. The polymer should be insoluble in situ, so that it remains in situ over a period of time, for instance at least several hours, days or weeks. A gel comprises a matrix of polymer and solvent distributed throughout the matrix. Preferably the solvent in the gel is aqueous and substantially free of organic solvent.
The gel depot may be used as a vehicle for delivery to the body cavity of therapeutically active agents, or diagnostic agents such as contrast agents. Contrast agents may, for instance, be introduced to allow medical practitioners to visualise the position of the insoluble polymer, which itself may be providing a therapeutic benefit, or diagnostic utility in a patient. According to a preferred aspect of the invention therefore the insoluble polymer is, in the body cavity, combined with a therapeutically active or imaging agent.
The gelled polymer may be a coating, or encapsulating agent, on particulate or non particulate solid material which is opaque to electromagnetic radiation (possibly radio frequency). The opaque material may, for instance, be an imaging agent such as described in U.S. Pat. No. 5,667,767 such as tantalum, tantalum oxide and barium sulphate, or as described in U.S. Pat. No. 5,695,480 including gold, tungsten and platinum. The opaque agent may be particulate or may be a solid material having a discrete physical shape, for instance being 1 mm or larger in size such as a metallic coil, filament, wire, mesh or tube. For instance coils as described in U.S. Pat. Nos. 4,994,069, 5,122,136, 5,226,911 or U.S. Pat. No. 5,702,361 may be included.
The present invention is particularly useful for embolising blood vessels, or for packing aneurysms. The polymer is thus used in methods analogous to those described in the prior art discussion above. The invention may also be used as a therapeutic or cosmetic filler, for instance for use following tumour excision, for enhancing lips or breasts, for improving muscle control, for instance sphincter muscles to control incontinence, for endoluminal gel paving, for the treatment of patent ductus arteriosus, or for replacement or supplement of synovial fluid.
The charged polymer is prior to insolubilisation, soluble, in the composition in which it is introduced into the body cavity. That composition is preferably aqueous. The polymer is thus preferably water-soluble. The counterion is also preferably soluble in the separate composition in which it is introduced into the body cavity. It is most convenient for the separate composition to be aqueous, so that it is preferred for the counterion to be introduced in a water-soluble form, in solution in an aqueous composition.
The two compositions may be mixed in the body cavity or immediately before being introduced into the body cavity. Preferably they are introduced using a catheter designed for the purpose, which has separate lumens for each composition and means for allowing contact and mixing of the compositions immediately before delivery of the insoluble, usually gel form, polymer from the catheter into the desired location in a body cavity.
The counterion may be inorganic or organic. It may be a di- or tri-valently charged soluble ion, for instance a metal cation, or a multivalent oxyanion. Calcium ions are suitable multivalent cations.
Preferably in the invention, the counterion is a polyelectrolyte. The counterionic charges of the two polymers attract one another when the polymers are intimately mixed, thereby insolubilising (gelling) the blend. This blend is consequently a polyion (or polyelectrolyte) complex. At least one of the polymers forming the polyion complex should have zwitterionic pendant groups. Preferably both polymers have zwitterionic pendant groups. The charged polymer which has an essential feature pendant zwitterionic groups, may be anionic or cationic but is preferably anionic. The counterion is thus preferably cationic.
In some embodiments of the present invention, a polycationic polymer will have permanently cationic pendant groups. These may be quaternary ammonium or phosphonium or tertiary sulphonium groups. In other embodiments, the cationic group may not be a permanent cation. It may be a weak or a strong base. For instance it may be selected so as to provide pH sensitivity whereby the degree of attraction between the two first polymers may be controlled by the pH.
Likewise, the anion may be the anion of a weak or strong acid, selected so as to be pH sensitive or insensitive within a predetermined pH range, as desired.
A suitable cationic group is a group N+R13, P+R13 or S+R12 
in which the groups R1 are the same or different and are each hydrogen, C1-4-alkyl or aryl (preferably phenyl) or two of the groups R1 together with the heteroatom to which they are attached from a saturated or unsaturated heterocyclic ring containing from 5 to 7 atoms. Preferably the cationic group is permanently cationic, that is each R1 is other than hydrogen. Preferably the cationic group is N+R13 in which each R1 is C1-4-alkyl, preferably methyl.
Suitable anionic groups are carboxylate, carbonate, sulphonate, sulphate, phosphonate or phosphate. Preferably the anionic group is monovalent. A sulphonate group is particularly convenient.
In a polyion complex used in the invention, the polycationic polymer and polyanionic polymer are preferably used in ratios so as to provide a ratio of equivalents of cationic groups and anionic groups in the range 2:1 to 1:2. Preferably the anions are present in approximately equivalent amount to the cation so that the ratio is preferably in the range 1.5:1 to 1:1.5, or preferably 1.2:1 to 1:1.2, for instance about 1:1.
In the gelled condition the level of zwitterionic groups is preferably in the range 1 to 75 mole %, preferably 20 to 50%, based on the total moles of monomer from which the polymer(s) forming the insoluble polymer are formed (in the preferred embodiment where the charged polymer(s) is formed from ethylenically unsaturated monomers including zwitterionic monomer).
The amount of ionic monomer in an ionic polymer comprised in the charged polymer is preferably at least 1 mole %, more preferably at least 5 mole %, for instance at least 10 mole %. Where the amount is higher than about 30 or 40 mole % (and the counterionic charges in a PIC are approximately balanced) the or each polymer should preferably also include at least 20%, preferably at least 30% zwitterionic monomer.
For the preferred embodiment in which the charged polymer comprises at least one ionically charged polymer including zwitterionic pendant groups, the ratio of zwitterionic ionic groups is preferably in the range 5:1 to 1:5, preferably 2:1 to 1:3.
The total content of ionic and zwitterionic monomer in the charged polymer and in preferred counterion is preferably at least 25 mole %, more preferably at least 30%, more preferably at least 40%, up to 100%, more preferably up to 80%, most preferably in the range 50 to 70%. The remaining components of the polymer(s) are non-ionic monomer, which may act primarily as diluent or may confer desirable physical properties on the polymer(s). A non-ionic, monomer may comprise a hydrophobic pendant group.
The ratio of anionic to cationic polymer and the relative amounts of zwitterionic and hydrophobic diluent groups in a polyion complex may be judged by determining the gel properties of a gel, usually an aqueous gel formed by mixing the counterionic polymers from solutions each containing one of the polymers. A suitable technique for investigating the gel properties is described in Example 3 below.
The zwitterionic pendant group of the polymer used in the invention may have an overall charge, for instance by having a divalent centre of anionic charge and monovalent centre of cationic charge or vice versa or by having two centres of cationic charge and one centre of anionic charge or vice versa. Preferably, however, the zwitterion has no overall charge and most preferably has a centre of monovalent cationic charge and a centre of monovalent anionic charge.
Preferably the centre of cationic charge in the zwitterionic group is permanent, that is it is preferably a quaternary ammonium or phosphonium or a tertiary sulphonium group. Preferably the anion is permanent, that is it is substantially completely ionised at in vivo pH""s, for instance at pH""s in the range 5 to 8. It is preferably a phosphate, phosphonate, sulphate or sulphonate anion.
The zwitterionic group may be a betaine group (ie in which the cation is closer to the backbone than the anion), for instance a sulpho-, carboxy- or phospho-betaine. A betaine group should have no overall charge and is preferably a carboxy- or sulpho-betaine. If it is a phosphobetaine the phosphate terminal group must be a diester, i.e., be esterified with an alcohol. Such groups may be represented by the general formula I
xe2x80x94X2xe2x80x94R2xe2x80x94N.(R3)2xe2x80x94R4xe2x80x94V⊕xe2x80x83xe2x80x83I
in which
X2 is a valence bond, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94, preferably xe2x80x94Oxe2x80x94;
V is a carboxylate, sulphonate or phosphate diester(monovalently charged) anion;
R2 is a valence bond (together with X2) or alkanediyl, xe2x80x94C(O)alkanediyl- or xe2x80x94C(O)NHalkanediyl preferably alkanediyl and preferably containing from 1 to 6 carbon atoms in the alkanediyl chain;
the groups R3 are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms or the groups R3 together with the nitrogen to which they are attached form a heterocyclic ring of 5 to 7 atoms; and
R4 is alkanediyl of 1 to 20, preferably 1 to 10, more preferably 1 to 6 carbon atoms.
One preferred sulphobetaine monomer has the formula II 
where the groups R5 are the same or different and each is hydrogen or C1-4 alkyl and n is from 2 to 4.
Preferably the groups R5 are the same. It is also preferable that at least one of the groups R5 is methyl, and more preferable that the groups R5 are both methyl.
Preferably n is 2 or 3, more preferably 3.
Alternatively the zwitterionic group may be an amino acid moiety in which the alpha carbon atom (to which an amine group and the carboxylic acid group are attached) is joined through a linker group to the backbone of polymer A. Such groups may be represented by the general formula III 
in which
X3 is a valence bond, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94, preferably xe2x80x94Oxe2x80x94,
R6 is a valence bond (optionally together with X3) or alkanediyl, xe2x80x94C(O)alkanediyl- or xe2x80x94C(O)NHalkanediyl, preferably alkanediyl and preferably containing from 1 to 6 carbon atoms; and
the groups R7 are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl, or two of the groups R7, together with the nitrogen to which they are attached, form a heterocyclic ring of from 5 to 7 atoms, or the three group R7 together with the nitrogen atom to which they are attached form a fused ring structure containing from 5 to 7 atoms in each ring.
Preferably the zwitterion has the formula IV 
in which
the moieties X4 and X5, which are the same or different, are xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94 or a valence bond, preferably xe2x80x94Oxe2x80x94, and
W+ is a group comprising an ammonium, phosphonium or sulphonium cationic group and a group linking the anionic and cationic moieties which is preferably a C1-12-alkanediyl group.
Preferably W contains as cationic group an ammonium group, more preferably a quaternary ammonium group.
The group W+ may for example be a group of formula xe2x80x94W1xe2x80x94N+R83, xe2x80x94W1xe2x80x94P+R93, xe2x80x94W1xe2x80x94S+R92 or xe2x80x94W1-Het+ in which:
W1 is alkanediyl of 1 or more, preferably 2-6 carbon atoms optionally containing one or more ethylenically unsaturated double or triple bonds, disubstituted-aryl, alkylene aryl, aryl alkylene, or alkylene aryl alkylene, disubstituted cycloalkyl, alkylene cycloalkyl, cycloalkyl alkylene or alkylene cycloalkyl alkylene, which group W1 optionally contains one or more fluorine substituents and/or one or more functional groups; and
either the groups R8 are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl, or aryl, such as phenyl or two of the groups R8 together with the nitrogen atom to which they are attached form a heterocyclic ring containing from 5 to 7 atoms or the three groups R8 together with the nitrogen atom to which they are attached form a fused ring structure containing from 5 to 7 atoms in each ring, and optionally one or more of the groups R8 is substituted by a hydrophilic functional group, and
the groups R9 are the same or different and each is R8 or a group OR8, where R8 is as defined above; and
Het is an aromatic nitrogen-, phosphorus- or sulphur-, preferably nitrogen-, containing ring, for example pyridine.
Preferably W1 is a straight-chain alkanediyl group, most preferably 1,2-ethanediyl.
Preferred groups of the formula IV are groups of formula V: 
where the groups R10 are the same or different and each is hydrogen or C1-4 alkyl, and m is from 1 to 4.
Preferably the groups R10 are the same. It is also preferable that at least one of the groups R10 is methyl, and more preferable that the groups R10 are all methyl.
Preferably m is 2 or 3, more preferably 2.
Alternatively the ammonium phosphate ester group V may be replaced by a glycerol derivative of the formula VB, VC or VD defined in our earlier publication no WO-A-93/01221.
Preferably the polymer or polymers having a pendant zwitterionic group are wholly synthetic, although under some circumstances it may be desirable to use derivatives of natural polymers. Preferably the polymer(s) is formed from radical polymerisable ethylenically unsaturated monomers including a monomer of the formula VI
YBXxe2x80x83xe2x80x83VI
wherein
B is a straight or branched alkanediyl, alkanediyloxaalkanediyl or alkanediyloligo(oxaalkanediyl) chain optionally containing one or more fluorine atoms up to and including perfluorinated chains or, if X or Y contains a terminal carbon atom bonded to B, a valence bond;
X is the zwitterionic group; and
Y is an ethylenically unsaturated polymerisable group selected from 
xe2x80x83CH2xe2x95x90C(R)xe2x80x94CH2xe2x80x94Oxe2x80x94, CH2xe2x95x90C(R)xe2x80x94CH2OC(O)xe2x80x94, CH2xe2x95x90C(R)OC(O)xe2x80x94, CH2xe2x95x90C(R)xe2x80x94Oxe2x80x94, CH2xe2x95x90C(R)CH2OC(O)N(R11)xe2x80x94, R12OOCCRxe2x95x90CRC(O)xe2x80x94Oxe2x80x94, RCHxe2x95x90CHC(O)Oxe2x80x94, RCHxe2x95x90C(COOR12)CH2xe2x80x94C(O)xe2x80x94Oxe2x80x94, 
xe2x80x83wherein:
R is hydrogen or a C1-C4 alkyl group;
R11 is hydrogen or a C1-C4 alkyl group or R11 is xe2x80x94Bxe2x80x94X where B and X are as defined above; and
R12 is hydrogen or a C1-4 allyl group or BX where B and X are as defined above;
A is xe2x80x94Oxe2x80x94 or xe2x80x94NR11xe2x80x94;
K is a group xe2x80x94(CH2)pOC(O)xe2x80x94, xe2x80x94(CH2)pC(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)Oxe2x80x94, xe2x80x94(CH2)pNR13xe2x80x94, xe2x80x94(CH2)pNR13C(O)xe2x80x94, xe2x80x94(CH2)pC(O)NR13xe2x80x94, xe2x80x94(CH2)pNR13C(O)Oxe2x80x94, xe2x80x94(CH2)pOC(O)NR13xe2x80x94, xe2x80x94(CH2)pNR13C(O)NR13xe2x80x94 (in which the groups R13 are the same or different), xe2x80x94(CH2)pOxe2x80x94, xe2x80x94(CH2)pSO3xe2x80x94, or, optionally in combination with B, a valence bond and p is from 1 to 12 and R13 is hydrogen or a C1-C4 alkyl group;
Preferably Y is a group CH2xe2x95x90C(R)COAxe2x80x94, in which R is H or methyl, preferably methyl, and in which A is preferably O.
B is preferably an alkanediyl group of 1 to 12, preferably 2 to 6 carbon atoms, most preferably group (CH2)q in which q is 2 to 6.
Where the polymer having a zwitterionic group is part of a polyion complex, the polymer is formed by including in the ethylenically unsaturated monomers an ionic monomer of the formula VII
Y1B1Qxe2x80x83xe2x80x83VII
in which
Y1 is selected from the same groups as Y;
B1 is selected from the same groups as B; and
Q is an ionic group or ionisable.
Q may be a cationic group Q1 or an anionic group Q2. A cationic group Q1 is preferably as described above. An anionic group Q2 is preferably selected from the groups listed above.
Another suitable type of cationic monomer copolymerisable with ethylenically unsaturated monomers is diallyl dialkyl ammonium halide, for instance diallyl dimethyl ammonium chloride.
The ethylenically unsaturated monomers preferably further comprise nonionic monomer. The nonionic monomer may be selected so as to confer desired solubility, hydrophilicity or hydrophobicity properties upon the polymer bearing zwitterionic pendant groups. The nonionic monomer may also confer on the polymer physical characteristics which affect the mechanical characteristics of the insoluble polymer in situ. For instance hydrophobic groups may provide inter or intramolecular interactions with other hydrophobic groups, or with substrates or biological compounds in situ which render the insoluble polymer particularly suitable for the desired application.
Preferably a nonionic monomer has the general formula VIII
Y2R14xe2x80x83xe2x80x83VIII
in which
Y2 is selected from the same groups as Y; and
R14 is a nonionic organic group which is an optionally substituted C1-24-alkyl or -alkenyl group. Optional substituents in the alkyl or alkenyl group are hydroxyl groups; halogen atoms, alkoxy and oligo-alkoxy groups, in which the alkoxy groups have 1-6, preferably 2 or 3 carbon atoms; aryl groups, preferably optionally substituted phenyl groups; optional substituents in a phenyl group being hydroxyl, halogen atoms or alkyl groups; acyl groups, especially C1-6-alkanoyl groups; acyloxy groups, especially C1-6-alkanoyloxy groups; acylamino groups, especially C1-6-alkanoyl amino, in any of which alkanoyl groups there may be substituents selected from halogen atoms and hydroxyl groups, and alkoxy groups. Preferred groups R14 are C1-24-unsubstituted alkyl, more preferably C4-18-alkyl.
A nonionic monomer is preferably present in the ethylenically unsaturated monomers from which the charged polymer and/or the counterionic polyelectrolyte are formed in a molar amount in the range 1-75%, preferably 20 to 70%, more preferably 30-50%.
A particularly preferred use of the invention is in the treatment of aneurysms. The charged polymer and counterion could be mixed via a catheter, in the form of aqueous solutions or dispersions, to form a gel in situ within the aneurysm void. Once filled the aneurysm would have no void space for the blood to occupy and the danger of rupture of the blood vessel would be removed.
The zwitterionic groups of the gelled (insoluble) polymer are believed to confer biocompatibility, minimising response from the inner lining of the aneurysm or other tissue or biological fluids in contact with the second polymer in the body cavity.